I too run diesel all the way to the back of my Di-Pricol gauge. When I first installed the FP gauge, I installed the isolater with it. But the gauge always showed 5 psi no matter what, it even took about 5 hrs. for the preesure to go back to zero after the truck was shut off. So I removed the isolater to see if that was the problem, and it was, so I just left it off. I have been running that way for about 23,000 miles.
At first the FP gauge buzzed and vibrated like crazy. So I read about installing a needle valve, so I installed it, and it did what it was supposed to do, stopped the buzzing. But then about 6 mo. ago I installed the Wildcat Max Flow Kit. At first I left the needle valve on there, and WOT pressure was about 9 psi. Then the valve developed a leak, so I took it off and reattached everything with out the needle valve, and guess what, WOT pressure went up 2 psi to 11 psi. I'm pretty sure that the valve was open enough, for it being too tight, to not be a problem. But after removing the valve the buzzing was back

. So I removed the stainless braided hose from the fuel filter to the VP44 ( my FP port is at the VP44 ), and replaced it with a rubber 3/8's fuel hose. The rubber fuel hose absorbs the vibration and the gauge is silent once again, only this time the FP reading is completely accurate. The only possible problem is that without the valve I have no way of shutting off the flow of fuel if I have a leak.
Sorry for the long story !
Jeff